STEM Mystery:

Decreasing Hedgehogs Mystery

Grades 6-8

Why are the hedgehogs disappearing?


Photo by Alexas_Fotos on Unsplash

The European Hedgehog is a common mammal found in many regions of Europe, and they live mainly in areas with hedges, trees, and grassland. They are popular with gardeners and benefit the health and survival of gardens because of their diet, which consists of insects and other invertebrates (see graph). They are nocturnal and hibernate during the winter months.

They do not have a lot of variation in their coloring, but this helps them blend into their habitat amongst plants. Hedgehogs have spines along their back that serve as great protection against predators including badgers and foxes. When threatened, they roll into a ball! They are about 15-30 centimeters (or 6-12 inches) in length.

Sadly, from about 2000 to 2020, the number of hedgehogs found in the United Kingdom has dropped by half. Why are the hedgehogs disappearing?

Source: Wembridge, D., Johnson, G., Al-Fulaij, N., & Langton, S. (n.d.). The state of Britain’s hedgehogs 2022 – Hedgehog Street. Retrieved April 2, 2022, from 

Career Education and Description

Being an Ecologist requires a bachelor’s degree in ecology or biology to begin. Depending on what you want to do, a master’s degree might be required.

Career description:
Ecologists study the way that living and non-living things interact in their environment. They collect data from multiple sources to paint a picture of the health of an ecosystem. From there, action plans can be created with local governments and the public to protect natural resources and ways to monitor progress.

Solving the Mystery

Which of the following are most likely to lead to the reason the hedgehog population has decreased? Use your worksheet to take notes, make observations and record conclusions.

PDF of Student Worksheet

Air Pollution

Average Concentrations of Air Chemicals in the U.K.

Pollution TypeDescription (known response in humans)199220002020
OzoneThe gas can cause irritation of the respiratory system. It can have damaging effects on plant life.53.969.367.9
Nitrous OxideThe gas can cause irritations of the respiratory system.59.635.714.5
ParticulatesThis covers a wide variety of small solids carried in the air that can be toxic.36.126.914.8
Source: GOV.UK. (2021, April 29). Air Quality Statistics. GOV.UK. Retrieved April 1, 2022, from 

Physical Barriers like Fences

Wooden fences are common in the U.K. to surround houses and other buildings. Building continues in the country, increasing steadily since 1992.

Photo by Daniel Janzen on Unsplash

Hedgehogs being Kept as Pets

Photo by Siem van Woerkom on Unsplash

Pet hedgehogs are African Pygymy hedgehogs. They usually do not grow beyond 25 centimeters (10 inches) and they come in a few different colors, like the white hedgehog in the picture.

Predation of Hedgehogs by Pets

Source: “Cats, Dogs and Hedgehogs.” Shropshire Wildlife Trust, 2021,


Are more hedgehogs getting hit by cars?

YearsHedgehog Casualties/100km of RoadTraffic Volume (billion vehicle – km/year
1990 – 1993 2.16 412
2001 – 2004 4.45 484
2015 – 2018 0.69 548
Source: Wembridge, D., Johnson, G., Al-Fulaij, N., & Langton, S. (n.d.). The state of Britain’s hedgehogs 2022 – Hedgehog Street. Retrieved April 2, 2022, from 

Loss of Vegetation

Source: Ukceh land cover maps. UK Centre for Ecology & Hydrology. (n.d.). Retrieved April 3, 2022, from 

*Graphic above does not include Ireland. See following graph for information on Ireland’s land changes.

Source: Land cover and land cover changes in European countries in 2000-2018. Copernicus. (2021, May 27). Retrieved April 3, 2022, from 

Changes in Weather

Graphs source: Kendon, M., Jevrejeva, S., Matthews, A., Sparks, T., & Garforth, J. (2021, July 28). State of the UK Climate 2020. Royal Meteorological Society. Retrieved April 3, 2022, from 


  • Idea and Writing: Tonya Schield
  • Editing: Gail Wheatley